Surgical Technique: Reversal of Anterior Cervical Fusion by Placement of an Artificial Disc Prosthesis
Surgical Overview and Discussion: Part 2
The procedure was performed from an anterior approach via an extension of the previous C5-6 transverse incision. Via an extensile approach the anterior vertebral body at C5-7 was exposed. The old plate was removed. The arthrodesis at C5-6 appeared solid. An anterior decompression was effected at the C6-7 level. A thorough foraminotomy at this level was effected bilaterally. A 16 mm Bryan disc prosthesis (Spinal Dynamics Corp., Mercer Island, WA) was then placed into this defect.
Attention then turned to the C5-6 space. Because there was no disc space that could be incised, fluoroscopic guidance was used to localize the likely position of the interbody graft. Using a high speed drill the bone graft was drilled out. Because the posterior longitudinal ligament had not been removed, it made localization of the canal significantly easier. The drilling continued to the uncovertebral joints and the end plates at this level were decorticated. It was clear that the graft had incorporated at this level but a degree of graft subsidence had occurred.
The key maneuver was then an attempt at distraction of the disc space using the cam distractors of the Bryan Disc cervical instrumentation set. When the cam distractor was placed and rotated, it was evidence that the C5 and C6 vertebrae moved independently; as suspected on the preoperative imaging fusion of the facet joints had not occurred. Consequently, a thorough decompression of both foramina and placement of a 17 mm prosthesis was effected. Intraoperative images after placement of the prostheses are shown below. Note the holes still present from the old plate:
Postoperatively the patient awoke well with full power in his limbs and resolution of the pain and weakness in both arms.
Postoperative imaging is shown below:
Repeat CT scanning at the C5-6 and C6-7 levels confirmed a very thorough foraminal and central decompression:
Flexion/Extension x-rays confirmed movement at the C5-6 and C6-7 level:
This is the first reported case of reversal of a previously arthrodesed segment in the cervical spine using an artificial disc prosthesis.
Preoperative and Postoperative X-Rays
Several points need to be made:
(a) Most fusions cannot be reversed once a solid arthrodesis has been achieved, especially if circumferential fusion has occurred. The key is the status of the facet joints.
(b) Placement of an artificial disc prosthesis may provide some protective effect to adjacent levels in terms of reducing the risk of developing accelerated adjacent segment disease.
(c) The long-term implications of placement of a Bryan disc cervical prosthesis are not known.
Nevertheless, the report illustrates the novel use of a new technology to reverse what was previously regarded as irreversible. Most cases that have attained solid fusion cannot be reversed and each case needs to be carefully evaluated by an experienced spine surgeon.